The invention relates to a multichamber-candle filter element for filtration of a residual volume of suspension with rapidly settling solid components and its assembly into a filter unit.
In European Patent Application EP-A-O 066 921, a candle filter element of the single chamber type is described. This type of filter element, which is usually suspended in a pressurized container, is suitable for, but limited to, residual volume filtration.
In Swiss Patent Application 658 401, the current filter elements are arranged in a pressurized container. A centrally positioned filter element, which extends up to the deepest point of a conical filter container, is used for residual volume filtration. The filter element is surrounded with a bell-shaped jacket. The unfiltered residual volume from the bottom of the filter container is forced by pressurized gas in the filter container into the space between the jacket and the filter means of the filter candle provided for that and is largely filtered out in this way. A remaining residual volume is still present after this residual volume filtration however, since the pressurized gas, e.g. air or an inert gas, penetrates through the filter candle with a minimum covering layer of fluid.
All known processes with candle filter elements have disadvantages, then above all, when the suspensions having a high solid components content must be filtered. Also on filtration of solid components from a suspension, which should not be comminuted or ground up and which have large grain size or a high specific gravity (of the suspension being filtered), problems occur.
Also a method based on spraying the residual volume into a container during an extended circulation by pumps. Here--the suspended solid particles are ground up--and thus damaged mechanically. The clogging of the spray nozzles can be viewed as an additional disadvantage. A washing of the filter cake and a subsequent discharge of the confined filter cake is difficult.
Furthermore, the solid components of the suspension to be filtered must be deposited on the filter candle element in a limited thickness. As a result, often very large filter surface areas are required according to the amount of the solid components to be separated from the suspension. The separated filter cake is then subjected to a further treatment, such as a washing and/or drying. Of course, no tears or cracks in the filter cake are permitted, otherwise the features of the treatment are incomplete.